Abrasive wheels which are both very thin and highly stiff are commercially important. For example, thin abrasive wheels are used in cutting off thin sections and in performing other abrading operations in the processing of silicon wafers and so-called pucks of alumina-titanium carbide composite in the manufacture of electronic products. Silicon wafers are generally used for integrated circuits and alumina-titanium carbide pucks are utilized to fabricate flying thin film heads for recording and playing back magnetically stored information. The use of thin abrasive wheels to abrade silicon wafers and alumina-titanium carbide pucks is explained well in U.S. Pat. No. 5,313,742, the entire disclosure of which patent is incorporated herein by reference.
As stated in the '742 patent, the fabrication of silicon wafers and alumina-titanium carbide pucks creates the need for dimensionally accurate cuts with little waste of the work piece material. Ideally, cutting blades to effect such cuts should be as stiff as possible and as thin as practical because the thinner the blade, the less waste produced and the stiffer the blade, the more straight it will cut. However, these characteristics are in conflict because the thinner the blade, the less rigid it becomes.
Industry has evolved to using monolithic abrasive wheels, usually ganged together on an arbor-mounted axle. Individual wheels in the gang are axially separated from each other by incompressible and durable spacers. Traditionally, the individual wheels have a uniform axial dimension from the wheel's arbor hole to its periphery. Although quite thin, the axial dimension of these wheels is greater than desired to provide adequate stiffness for good accuracy of cut. However, to keep waste generation within acceptable bounds, the thickness is reduced. This diminishes rigidity of the wheel to less than the ideal.
The conventional straight wheel is thus seen to generate more work piece waste than a thinner wheel and to produce more chips and inaccurate cuts than would a stiffer wheel. The '742 patent sought to improve upon performance of ganged straight wheels by increasing the thickness of an inner portion extending radially outward from the arbor hole. It was disclosed that a monolithic wheel with a thick inner portion was stiffer than a straight wheel with spacers. However, the '742 patent wheel suffers from the drawback that the inner portion is not used for cutting, and therefore, the volume of abrasive in the inner portion is wasted. Because thin abrasive wheels, especially those for cutting alumina-titanium carbide, employ expensive abrasive substances such as diamond, the cost of a '742 patent wheel is high compared to a straight wheel due to the wasted abrasive volume.
It is desirable to have a straight, monolithic, thin abrasive wheel having enhanced rigidity compared to conventional wheels. Aside from wheel geometry, rigidity is determined by the intrinsic stiffness of the materials of wheel construction. Monolithic wheels are made up basically of abrasive grains and a bond which holds the abrasive grains in the desired shape. Heretofore, a metal bond normally has been used for thin abrasive wheels intended for cutting hard materials such as silicon wafers and alumina-titanium carbide pucks. A variety of metal bond compositions for holding diamond grains, such as copper, zinc, silver, nickel, or iron alloys, for example, are known in the art. It now has been discovered that addition of at least one active metal component to a metal bond composition can cause the diamond grains to chemically react with the active metal component during bond formation thereby forming an integrated, grain-reinforced composite. The very high intrinsic stiffness of the grains together with the chemical bond of the grains to the metal thus produce a substantially increased stiffness abrasive structure.
Accordingly, the present invention provides an abrasive wheel comprising a straight, monolithic, grain-reinforced abrasive disk having a uniform width in the range of about 20-2,500 .mu.m, consisting essentially of about 2.5-50 vol. % abrasive grains and a complemental amount of a bond comprising a metal component and an active metal which forms a chemical bond with the abrasive grains on sintering, the active metal being present in an amount effective to produce an elastic modulus of the grain-reinforced abrasive disk at least 10% higher than the elastic modulus of a sintered disk of same composition but free of active metal.
There is also provided a method of cutting a work piece comprising the step of contacting the work piece with an abrasive wheel comprising a straight, monolithic, grain-reinforced abrasive disk having a uniform width in the range of about 20-2,500 .mu.m, consisting essentially of about 2.5-50 vol. % abrasive grains and a complemental amount of a bond comprising a metal component and an active metal which forms a chemical bond with the abrasive grains on sintering, the active metal being present in an amount effective to produce an elastic modulus of the grain-reinforced abrasive disk at least 10% higher than the elastic modulus of a sintered disk of same composition but free of active metal.
Further this invention provides a method of making an abrasive tool comprising the steps of
(a) providing preselected proportions of particulate ingredients comprising PA1 (b) mixing the particulate ingredients to form a uniform composition; PA1 (c) placing the uniform composition into a mold of preselected shape; PA1 (d) compressing the mold to a pressure in the range of about 345-690 MPa for a duration effective to form a molded article; PA1 (e) heating the molded article to a temperature in the range of about 500-900.degree. C. for a duration effective to sinter the metal component and active metal to a sintered bond, thereby integrating the abrasive grains and sintered bond into a grain-reinforced composite; and PA1 (f) cooling the grain-reinforced composite to form the abrasive tool.
(1) abrasive grains; PA2 (2) a metal component consisting essentially of a major fraction of copper and a minor fraction of tin; and PA2 (3) an active metal which can form a chemical bond with the abrasive grains on sintering;